Add support for client certificate and private key #1235

Job	Run time
compile-examples (arduino:mbed:nano33ble, nano33ble)	7m 41s
compile-examples (arduino:mbed:envie_m7, envie_m7)	30m 3s
compile-examples (arduino:mbed:envie_m7:target_core=cm4, envie_m7_core_cm4)	5m 58s
compile-examples (arduino:mbed:nanorp2040connect, nanorp2040connect)	12m 46s
compile-examples (arduino:mbed:nicla_sense, nicla_sense)	13m 44s
compile-examples (arduino:mbed:nicla_vision, nicla_vision)	17m 5s
compile-examples (arduino:mbed:opta, opta)	20m 17s
compile-examples (arduino:mbed:giga, giga)	28m 23s
compile-examples (arduino:mbed:nicla_voice, nicla_voice)	5m 22s
compile-examples (arduino:mbed:edge_control, edge_control)	6m 12s
	2h 27m 31s

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